Media productions such as motion pictures, television shows, television commercials, videos, multimedia CD-ROMs, web productions for the Internet/intranet, and the like have been traditionally created through a three-phase process: pre-production 11, production 12, 13 and post-production 14 as illustrated in FIG. 1. Pre-production 11 is the concept generation and planning phase. In this phase, scripts and storyboards are developed, leading to detailed budgets and plans for production 12, 13 and post-production 14. Production 12, 13 is the phase for creating and capturing the actual media elements used in the finished piece. Post-production combines and assembles these individual elements, which may have been produced out of sequence and through various methods, into a coherent finished result using operations such as editing, compositing and mixing.
During the production phase, two distinct categories of production techniques can be used, live/recorded production 12 and synthetic production 13.
The first category, "live/recorded media production 12", is based on capturing images and/or sounds from the physical environment. The most commonly used techniques capture media elements in recorded media formats such as film, videotape, and audiotape, or in the form of live media such as a broadcast video feed. These media elements are captured through devices like cameras and microphones from the physical world of actual human actors, physical models and sets. This requires carefully establishing and adjusting the lighting and acoustics on the set, getting the best performance from the actors, and applying a detailed knowledge of how the images and sounds are captured, processed and reconstructed.
As live/recorded media elements are captured, they are converted into sampled representations, suitable for reconstruction into the corresponding images and sounds. Still images are spatially sampled: each sample corresponds to a 2D region of space in the visual image as projected onto the imaging plane of the camera or other image capture device. Note that this spatial sampling is done over a specific period of time, the exposure interval. Audio is time-sampled: each sample corresponds to the level of sound "heard" at a specific instance in time by the microphone or other audio capture device. Moving images are sampled in both space and time: creating a time-sampled sequence of spatially-sampled images, or frames.
Sampled media elements can be represented as analog electronic waveforms (e.g. conventional audio or video signals), digital electronic samples (e.g. digitized audio or video), or as a photochemical emulsion (e.g. photographic film). The sampled live/recorded media elements are reconstructed as images or sounds by reversing the sampling process.
The second category of production techniques, synthetic media production 13, uses computers and related electronic devices to synthetically model, generate and manipulate images and sounds, typically under the guidance and control of a human operator. Examples of synthetic media production include computer graphics, computer animation, and synthesized music and sounds. Synthetic media uses synthetic models to construct a representation inside a computer or other electronic system, that does not exist in the natural physical world, for output into a format that can be seen or heard. Synthetic images are also called computer-generated imagery (CGI).
Synthetic media models are mathematical, geometric, or similar conceptual structures for generating images and/or sounds. They can be represented in software, hardware (analog circuits or digital logic), or a combination of software and hardware. These models specify, explicitly or implicitly, sequences of electronic operations, digital logic, or programmed instructions for generating the media elements, along with their associated data structures and parameters.
Synthetic media models are converted into actual images or sounds through a synthesis or "rendering" process. This process interprets the underlying models and generates the images and/or sounds from the models. Unlike sampled media elements, a synthetic media element can generate a wide range of different but related images or sounds from the same model. For example, a geometric model can generate visual images from different viewpoints, with different lighting, in different sizes, at different resolutions (level of detail). A synthetic musical composition can generate music at different pitches, at different tempos, with different "instruments" playing the notes. In contrast, live/recorded media elements can only reconstruct images or sounds derived from the samples of the original captured image or sound, though perhaps manipulated as, for example, for optical effects.
Creating synthetic models can be very labor-intensive, requiring considerable attention to detail and a thorough understanding of the synthetic modeling and rendering process. Synthetic models can be hierarchical, with multiple constituent elements. For example, a synthetic model of a person might include sub-models of the head, torso, arms and legs. The geometric, physical, acoustical and other properties, relationships and interactions between these elements must be carefully specified in the model. For animated synthetic media elements, the models typically include "motion paths": specifications of the model's movement (in 2D or 3D) over time. Motion paths can be specified and applied to the entire model, or to different constituent parts of hierarchical models.
To increase the perceived realism of a rendered synthetic element, the structure of a synthetic model may incorporate or reference one or more sampled media elements. For example, a synthetic geometric model may use sampled image media elements as "texture maps" for generating surface textures of the visual image (e.g. applying a sampled wood texture to the surfaces of a synthetic table). In a similar manner, sampled sound elements can be used to generate the sounds of individual notes when rendering a synthetic model of a musical composition. Within synthetic media production, there is an entire sub-discipline focused on capturing, creating and manipulating these sampled sub-elements to achieve the desired results during rendering. (Note that these sampled sub-elements may themselves be renderings of other synthetic models.)
Synthetic media is based on abstract, hierarchical models of images and sounds, while live/recorded media is based on sampled representations of captured images and sounds. Abstract hierarchical models allow synthetic media elements to incorporate sub-elements taken from live/recorded media. However, the reverse is not possible. The sampled representation of a live/recorded media cannot include a synthetic model as a sub-element. This is the key difference between reconstructing a live/recorded media element from its samples, and rendering a synthetic media element from its model.
While synthetic media elements are arguably more versatile than live/recorded media elements, they are limited in modeling and rendering truly "realistic" images and sounds. This is due to the abstract nature of the underlying synthetic models, which cannot fully describe the details and complexities of the natural world. These limitations are both theoretical (some natural phenomena cannot be described abstractly) and practical. The time, effort and cost to model and render a highly realistic synthetic media element can vastly outweigh the time, effort and cost of capturing the equivalent real image or sound.
Because a sampled media element has a very simplified structure (a sequence of samples) and contains no abstract hierarchical models, the process of capturing and then reconstructing a sampled media element is typically very efficient (usually real-time) and relatively inexpensive. In comparison, the process of modeling and then rendering a synthetic media element can be very time-consuming and expensive. It may take many minutes or hours to render a single synthetic visual image using modern computer-based rendering systems. Properly modeling a synthetic visual element might take a skilled operator anywhere from several minutes, to hours or weeks of time.
In summary, the processes and techniques used in synthetic media production 13 are very different from those used in live/recorded media production 12. Each produces media elements that are difficult, costly or even impossible to duplicate using the other technique. Synthetic media production 13 is not limited or constrained by the natural physical world. But synthetic techniques are themselves limited in their ability to duplicate the natural richness and subtle nuances captured in live/recorded media production 12.
Therefore, it has become highly advantageous to combine both types of production techniques in a media production. Each technique can be used where it is most practical or cost effective, and combinations of techniques offer new options for communication and creative expression.
Increasingly, producers and directors of media productions are creating scenes where multiple elements (synthetic and/or live/recorded elements) appear to be interacting with each other, co-existing within the same real or imagined space. They also want to apply synthetic techniques to manipulate and control the integration of separately produced live/recorded media elements. These new techniques can create attention-grabbing special effects: synthetic dinosaurs appearing to interact with human actors, synthetic spaceships attacking and destroying familiar cities, the meow of a cat replaced by the simulated roar of a dozen lions. There is also growing demand for more subtle, barely noticeable, alterations of reality: an overcast day turned into bright sunlight, scenery elements added or removed, or seamless replacements of objects (e.g. a can of soda held by an actor replaced with a different brand).
These "hybrid" media productions require combining separately produced media elements as if they were produced simultaneously, within a single common physical or synthetic space. This includes the need for bridging between production techniques that are done separately and independently, perhaps with entirely different tools and techniques. The requirements of hybrid productions place new requirements on all three phases of the production process (pre-production 11, production 12, 13, and post-production 14) that are time-consuming, labor-intensive and costly. In pre-production 11, careful planning is required to ensure that all media elements will indeed look as if they belong in the same scene. During production 12, 13, media elements must be created that appear to co-exist and interact as if they were captured or created at the same time, in the same space, from the same viewpoint. In post-production 14, the elements need to be combined (or "composited") to generate believable results: by adjusting colors, adding shadows, altering relative sizes and perspectives, and fixing all of the inevitable errors introduced during independent and often very separate production steps.
In some hybrid productions, the same object is represented as both a live/recorded and a synthetic media element. This allows the different representations to be freely substituted within a scene. For example, a spaceship might be captured as a live/recorded media element from an actual physical model and also rendered from a synthetic model. In shots where complex maneuvering is required, the synthetic version might be used, while the captured physical model might be used for detailed close-ups. The transitions between the physical and synthetic versions should not be noticeable, requiring careful matching of the geometry, textures, lighting and motion paths between both versions which have been produced through entirely separate processes.
These new requirements for hybrid productions require a new approach to the tools and processes used in media production. Today, the task of combining different media elements is commonly done through editing, layered compositing and audio mixing. All are typically part of the post-production process (or the equivalent final stages of a live production).
In today's process, each visual media element is treated as a sequence of two-dimensional images much like a filmstrip. Each audio element is treated as much like an individual sound track in a multi-track tape recorder. Live/recorded media elements can be used directly in post-production, while synthetic media elements must first be rendered into a format compatible with the live/recorded media elements.
Editing is the process of sequencing the images and sounds, alternating as needed between multiple live/recorded media elements and/or rendered synthetic elements. For example, an edited sequence about comets might start with an recorded interview with an astronomer, followed by a rendered animation of a synthetic comet, followed by recorded images of an actual comet. In editing, separate media elements are interposed, but not actually combined into a single image.
Layered compositing combines multiple visual elements into a single composite montage of images. The individual images of a visual media element or portions thereof are "stacked up" in a series of layers and then "bonded" into a single image sequence. Some common examples of layered compositing include placing synthetic titles over live/recorded action, or placing synthetic backgrounds behind live actors, the familiar blue-screen or "weatherman" effects. More complex effects are built up as a series of layers, and individual layers can be manipulated before being added to the composite image.
Audio mixing is similar to layered compositing, mixing together multiple audio elements into a single sound track which itself becomes an audio element in the final production.
Today's editing, mixing and layered compositing all assume a high degree of separation between live/recorded 12 and synthetic 13 production processes, waiting until post-production to combine the synthetic elements with the live/recorded elements. Since editing is inherently a sequencing operation, there are few problems introduced by the separation during production of live/recorded and synthetic elements.
However, the techniques used in layered compositing place severe restrictions on how different visual elements can be combined to achieve realistic and believable results. Building up an image sequence from multiple layers introduces a "layered look" into the finished material. It becomes very difficult to make the various media elements appear to "fit in" within composited images, as if they all co-existed in the same physical space. Differences in lighting and textures can be very apparent in the composited result.
Making the media elements appear to actually interact with each other adds additional levels of complexity. In a layered technique, the different media elements are necessarily in distinct layers, requiring considerable manual intervention to make them appear to realistically interact across their respective layers. If objects in different layers are moving in depth, layers must be shuffled and adjusted from frame to frame as one object moves "behind" the other, and different parts of each object must be adjusted to appear partially occluded or revealed. When this technique produces unacceptable results, the operator must attempt further iterations, or resort to manually adjusting individual pixels within individual frames, a process called "painting," or accept a lower quality result.
Substituting between different versions of the same object, which may include both live/recorded version(s) and rendered synthetic version(s), is equally difficult. This type of substitution should appear to be seamless, requiring careful and detailed matching between the "same" elements being mixed (or dissolved) across separate compositing layers. The human eye and ear are very sensitive to any abrupt changes in geometry, position, textures, lighting, or acoustic properties. Making the substitution look right can require multiple trial-and-error iterations of synthetic rendering and/or layered compositing.
These problems result from the traditional separation between live/recorded production 12 and synthetic production 13, along with the traditional separation of both types of production from the post-production process 14. Today, both types of production generate a sequence of flattened two-dimensional images taken from a specific viewpoint. Only the final sequences of 2D images are taken into the post-production process 14.
Even though the physical set of a live/recorded production 12 is inherently three-dimensional, the captured result is a 2D image from the camera's perspective. Similarly, many synthetic media tools are based on computer-generated 3D geometry but the resultant images are rendered into sequences of 2D images from the perspective of a "virtual camera". Any information about the relative depths and physical (or geometric) structure of objects has been lost in the respective imaging processes. There is little or no information about the relative position and motion of objects, of their relationships to the imaging viewpoint, or of the lighting used to illuminate these objects.
Then, in post-production 14, these 2D image sequences must be artificially constructed into simulated physical interactions, believable juxtapositions, and three-dimensional relative motions. Since the different visual elements were created at different times, often through separate and distinct processes, and exist only as sequences of 2D flattened images, this is extremely challenging.
Overcoming these problems using layered compositing is labor-intensive, time consuming and expensive. The images to be manipulated must be individually captured or created as separate layers, or separated into layers after production using techniques such as matting, image tracking, rotoscoping and cut-and-paste. Complex effects require dozens or even hundreds of separate layers to be created, managed, individually manipulated and combined. Information about depths, structures, motions, lighting and imaging viewpoints must be tracked manually and then manually reconstructed during the compositing process.
Interactions between objects must be done individually on each object within its own layer, with three-dimensional motions and interactions adjusted by hand. Manual labor is also required to simulate the proper casting of shadows, reflections and refractions between objects. These are also typically created by hand on every affected layer on every individual frame.
Consider a scene where a recorded actor grabs a synthetic soda can and throws it into a trash barrel. In each frame, the position of every finger of the hand needs to be checked and adjusted so that it appears to wrap around the soda can. The synthetic soda can has to show through the space between the fingers (but not "bleed through" anywhere else), and move as if it were being picked up and tossed out. As the can travels to the trash barrel, it must properly occlude various objects in the scene, cast appropriate shadows in the scene, land in the barrel, and make all the appropriate sounds.
The common solution to many of these problems is to separate each of the affected images into its own image layer, and then individually paint and/or adjust each of the affected images within each and every one of the affected layers. This involves manual work on each of the affected layers of the composited image, often at the level of individual pixels. In a feature film, each frame can have up to 4,000 by 3,000 individual pixels at a typical frame rate of 24 frames per second. In a TV production, at about 30 frames per second, each frame can have approximately 720 by 480 individual pixels. The required manual effort, and artistic skill, can result in man-months of work and tens of thousands of dollars expended in post-production 14.
Similar problems exist in audio mixing. The human ear is very sensitive to the apparent "placement" of sounds so that they correspond with the visual action. In a visual image produced with layered compositing, the movement of objects in the composited scene needs to be reflected in the audio mix. If an object goes from left to right, forward to back, or goes "behind" another object, the audio mix needs to reflect these actions and resulting acoustics. Today, all of this is done primarily through manual adjustments based on the audio engineer viewing the results of layered compositing. If the layered composite is altered, the audio must be re-mixed manually.
If the result is not acceptable, which is often the case, the same work must be done over and over again. The process becomes an iterative cycling between synthetic rendering, layered compositing (or audio mixing) and pixel painting (or adjusting individual audio samples) until the result is acceptable. In fact, for a high quality production, the iterations may include the entire project, including reconstruction and reshooting a scene with live action.